Door latch devices for vehicles include those, each in which an interlocking unit assembly is integrated with an operating unit assembly; the interlocking unit assembly including a body fixed to a door and made of synthetic resin, a latch accommodated in the body and engageable with a vehicle body side striker, and an interlocking mechanism, such as a pawl, engageable with the latch; and the operating unit assembly including a casing fixed to a reverse side of the body and made of synthetic resin, and an operating mechanism, which is installed in the casing, and which is able to switch over the door between a locked state and an unlocked state by the interlocking mechanism being operated (see, for example, Patent Literatures 1 and 2).
Such door latch devices include those, which do not have any lock knobs and key cylinders for security reasons, and which perform door locking/unlocking switch over only by electric operations. Such a door latch device includes an emergency lock mechanism that is able to lock a door by a key operation in order to avoid the door from becoming unlockable due to an electric system failure.